Looking at the British Airways Boeing in Johannesburg airport, pilots around the world are muttering "there but for the grace of God....". Everyone has taken a wrong taxi-way at some stage in their flying career. Embarrassment is usually the only damage when it comes to smaller aircraft and provided that active runways are not involved. For airline pilots and big jets, the consequences can be much greater .

At first glance the incident at OR Tambo International looks simple. It appears to have resulted from a mixture of human error and misfortune. The elderly jumbo jet, registered G-BNLL, missed a turn and went astray as it was taxiing from the terminal towards the threshold of runway 03 Left, where it would await its turn to take off. The danger lurking on its route was well known and the subject of a large warning printed on the airport chart.

All taxiways at airports are designated by a letter, while runways have numbers. At big airports the layout can be confusing, especially in the dark and poor visibility. Pilots use a map, or a "plate" -- now often electronic -- that shows the network of tracks weaving to and from the runways. Their task is to identify the correct taxiway and track the yellow centre line, often lit by embedded green lights. At big airports controllers sometimes have ground radar to check that aircraft are correctly following their instructions. As a precaution, the pilot flying is supposed to cross-check with the co-pilot that they are entering the right taxiways.

In the case of the BA Boeing, instead of following the curved taxiway Bravo, as instructed by the ground control, the pilots missed the left-hand bend and carried on straight ahead into a narrow lane, designated Mike. The wing sliced into the nearby maintenance building. If the building had not been there, the crew could have recognised the error and stopped and waited for help to get back onto the right runway. That would have resulted in an inquiry but no damage.

The potential danger of following this route at Johannesburg is clearly spelled out for pilots in the airport chart. In bold print, it says: "Aircraft to exercise caution when taxiing on taxiway B southbound to threshold Runway 03L due to Apron taxi-lane M extending from taxiway B in a Southerly direction."

The crew are unlikely to escape blame. Irrespective of which pilot was steering, the captain holds ultimate responsibility for the safety of the airliner. It is always possible but highly unlikely that the ground controller instructed the big jet onto the impossibly narrow taxiway. Mitigating factors could include the dark, poor lighting in the apron area, or possibly confusing or misunderstood instructions from the ground controllers.

Investigators will be looking at the speed of the airliner. Crews are supposed to move slowly manoeuvering in close quarters to other aircraft and buildings, but time pressures can sometimes lead to excessive speed.

The incident of Golf-double Lima is an illustration of why pilots will tell you they are more relaxed in the air -- the medium for which their craft are designed -- rather than steering their ungainly machines around the ground.